Slant 6 Head Gasket Question

The front coolant ports should be blocked by the head gasket...this is for sure. This is designed so that it forces all the coolant flow to go from front to back in the block, and then up into the head in the rear, and back to front through the head. In this way, all parts of the head and block receive cooling flow.

It is common on the old steel shim gaskets for the gasket to rust through up front and allow the coolant to bypass part of the head and block, which is not good.

Once back together, then take it easy and see if it tends to overheat again. Then come back and work on the issue. BTW, did you pull the block drain plug and flush it all out real good? This would be a good time to pull off the water pump and look into the block to see if it is full of crud.